Whole Foods has become the first grocery store in the nation to require labeling of GMO foods.

Big news for people concerned about avoiding genetically modified organisms (GMOs): Whole Foods, the nation's largest natural and organic foods retailer, has just announced that by 2018, all products sold in its stores must indicate whether they contain GMOs.

"We're responding to our customers, who have consistently asked us for GMO labeling and we are doing so by focusing on where we have control: in our own stores," said Walter Robb, co-CEO of Whole Foods Market, in a statement about the company's move.

The move could have a huge impact on the U.S. food system. Approximately 90 percent of all corn, soy, and canola grown in the U.S. is genetically modified, that is, it's had its DNA altered to withstand high levels of pesticides that kill weeds and insects. Genetically modified sugar beets, which are used to create most of the added sugars used in processed foods, make up 95 percent of the U.S. sugar beet crop. These genetically altered ingredients exist in more than 80 percent of all processed foods.

"The prevalence of GMOs in the U.S. paired with nonexistent mandatory labeling makes it very difficult for retailers to source non-GMO options and for consumers to choose non-GMO products," added Robb. The only guarantee that you're getting food free of GMOs is to buy certified-organic foods, which can be cost-prohibitive, or to find products certified by the nonprofit Non-GMO Project, which tests organic and nonorganic foods alike for the presence of GMOs. Though a stringent certification, it isn't very common.

Now that Whole Foods has made labeling mandatory, finding GMO-free foods could become a lot easier. It's currently the eighth-largest grocery chain in the U.S. with $11.8 billion in annual sales. And the labeling will appear not just on packaged dry goods, but also on dairy and meat products sourced from animals that may have been fed GMO grains. Food companies that wish to sell their products at the store will likely reformulate all their products sold in other stores as well, since they won't want to make different products to sell at different stores.

"This is going to have a huge impact on the food industry as a whole," says Doug Foreman, founder of Beanitos, a line of non-GMO-certified chips made from beans. He doesn't foresee Whole Foods losing tons of product lines due to the new requirement, but he does suspect a few brands will probably stop selling their products there, simply because the supply chain for non-GMO ingredients currently is very limited. And a product stamped as containing GMOs carries with it a negative image. "But the bigger picture, and one that Whole Foods completely understands, is that the growers and suppliers will have to change if they want the business, thus changing the supply chain across the board."

Labeling of GMOs has always been popular among the public—numerous surveys show that upwards of 92 percent of Americans want it—but highly unpopular among food and biotechnology companies, who, combined, spent $46 million dollars to defeat a ballot initiative in California that would have required that GMOs be labeled. Right now, similar legislation is moving through the legislatures of 20 states, but no labeling law has passed successfully, thus far, because these large agribusinesses threaten lawsuits that scare cash-strapped governors and legislators into vetoing the laws or voting them down.

The federal government has remained silent on the issue. And this announcement, says Ken Cook, president of the pro-labeling nonprofit Environmental Working Group, "will put new pressure on the Obama administration to fulfill the promise that then-presidential candidate Barack Obama made in 2007," referring to the statements President Obama made during his first campaign about requiring GMO labeling if elected.

"The best part is that Whole Foods has the right to require this in their stores, no law needed," says Foreman, "and there isn't a damn thing Monsanto can do to stop it," referring to the largest producer of GMO seeds and the pesticides they're designed to resist.

Whole Foods' labeling requirements will be rolled out over the next five years. If you're wondering why this is such a big deal, here are five quick and dirty facts about why you don't want to eat GMOs:

1. The pesticides that GMOs are bred to resist have been linked to a wide variety of health problems, including cancer, diabetes, developmental disorders, and even memory loss and food allergies. And those are just some of the 9 Crazy Things Pesticides Are Doing to Your Body.

2. Even though GMOs were intended to help farmers reduce their use of pesticides, farmers are now using more. A Washington State University study found that pesticide use has increased 7 percent since GMOs were first planted in 1996.

3. And that number is likely to continue to rise. The rampant use of herbicides and insecticides has led to a proliferation of "superweeds" and "superbugs" that no longer die when exposed to these toxic chemicals.

4. They're killing butterflies! A study from Cornell University found that the pollen from insect-resistant varieties of GMO corn kills monarch butterfly larvae. In addition to being beautiful insects, monarchs are considered a "flagship" species for conservation, which means that if something is harming them, other species could start suffering severe problems.

5. GMOs don't deliver on their promises. GMOs are often touted as miracle solutions to "feed the world" because they supposedly produce higher yields. But the Rodale Institute, a nonprofit organic farming research institution, has found in side-by-side farming trials that GMO crop yields are no higher than conventional or organic crop varieties.